1. Technical Field
The invention relates to a valve for use in pressure relief applications. More particularly, the invention relates to a pressure relief valve for use with inflatable devices where the valve provides super high and efficient exhaust capabilities. Specifically, the invention is a low profile pressure relief valve of a "pop action" design for instantaneous over-pressure exhausting at very high flow rates where the poppet assembly further includes a protected skirt around the poppet seal for an enhanced "pop action" providing improved flow rates.
2. Background Information
In recent years, the use of and demand for inflatable devices has grown significantly. Inflatable devices are now commonly used by the military, shipping and airline industries in such specific applications as life rafts and escape slides.
It is highly recommended and often required that at least one pressure relief valve (PRV) be installed on these inflatable devices to provide for over-pressure exhausting. Occasionally, these inflatable devices are inflated to a pressure greater than the recommended maximum pressure for the particular inflatable device. Over-inflation, which may damage or burst the inflation device thereby subjecting the surrounding environment and persons to possible damage and injury, is prevented by this over-pressure exhausting. This release of the fluid contents returns the inflation device to a safe working pressure.
These pressure relief valves have been in use with inflation devices for many years. Generally, two different classes of these pressure relief valves are used by the inflatable device industry. The first class being an older or "conventional" PRV, often referred to as a low or medium flow PRV. These low/medium flow PRVs provide a gradual valve opening during exhausting. The second class of PRVs is the newer "pop action" PRV, often referred to as a high flow PRV. These high flow PRVs provide an initially gradual and partial opening followed by a "pop action" or rapid complete opening that permits rapid and high flow exhausting.
A common low/medium flow PRV is shown in FIGS. 6-7. These low/medium flow PRVs have a low profile design with a poppet assembly that is fully housed within the valve so as to be protected from external damage. These low/medium flow PRVs generally supply reasonable exhaust rates of approximately 10 to 20 cfm at pressures of 3.0 to 3.5 psi.
In many applications, significantly higher exhaust flow rates per valve are desirable in order to minimize the number of PRVs required to manage the potential over-pressure within an inflatable device. The invention of high flow PRVs met this demand. One type of high flow PRV, often referred to as a bonneted PRV, is shown in FIGS. 8-9. The bonneted PRV modified the low/medium flow PRV by redesigning the upper throat by adding a capped or a bonneted configuration which results in "pop action" over-pressure exhausting. This "pop action" significantly improved exhausting. The exhaust flows achieved by high flow PRVs were often as high as 40 cfm or more at pressures of approximately 3.5 psi.
However, the bonnet of the high flow PRVs extends above the valve body exposing the bonnet to damage from the external environment. A protective cage was thus added to the high flow PRVs to protect the poppet assembly. These protective cages and to a lesser degree these bonnets add undesirable height and bulk to the overall valve assembly. In response, internal poppet PRVs with "pop action" were developed such as the PRV shown in FIGS. 10-11 and described in more detail in U.S. Pat. No. 4,142,549.
These internal poppet PRVs as shown in FIGS. 10-11 were successful in maintaining the high exhaust flow expected of high flow PRVs while protecting the poppet assembly from damage. However, the industry continued to seek high flow capabilities coupled with the lowest feasible overall valve profile. In response, Mirada Research and Manufacturing in the mid-1980s reduced the height of these internal "pop action" PRVs by moving the spring in between the inflatable device and the poppet rather than extending outward from the poppet as shown in the '549 patent.
Although this Mirada.TM. High Flow PRV functions efficiently and provides a compact valve design that has generally been the industry standard for a decade or more, higher flow rates at reduced valve opening pressures continue to be a desirable objective. The reason for this objective is twofold.
First, the industry prefers valves with standard exhausting pressures of below 3.0 psi since this assures less stress on the raft or slide fabric, particularly on the seams thereof. The current designs typically offer either no flow or only low flow exhausting prior to reaching 2.5 to 3.0 psi. Therefore, although many of the current designs offer high flow, it is at a pressure of typically 3.0 to 4.0 psi, which is higher than preferred by the industry. As a result, the industry clamors for high flow at lower yet reliable exhausting pressures.
The importance of high flow coupled with lower and reliable exhausting pressures is especially critical whenever the raft or slide is to be used in a warm climate. The fluid supply for the raft or slide is filled under conditions unrelated to and often dissimilar from actual use conditions. The actual volume of fluid in actual use conditions is directly correlated to temperature since volume, pressure and temperature of any fluid are all interrelated and defined. It is well-known that as the atmospheric temperature rises that the pressure or volume rises if the other is held constant. The result in the raft and slide industry is that the fluid supply in a warm climate, such as one exceeding 100.degree. F., is always excessive thus requiring exhausting during and/or after inflation. This cannot be overcome by reducing the initial fluid supply because this supply would then be deficient when the raft or slide is deployed in a cold climate, such as in Canada where the temperatures may reach -40.degree. F. or below. It is thus critical that rafts and slides both fully inflate at all temperatures including sub-zero and tropical temperatures and include relief mechanisms for allowing pressure relief at tropical temperatures.
Second, a sufficient increase in the flow rate directly decreases the quantity of PRVs needed on larger flotation devices which presently include multiple PRVs. This, of course, directly reduces raft or slide production costs as well as maintenance costs.
In response to these objectives, Mirada modified its "High Flow PRV" to include approximately twice as many ports (16 instead of the industry standard of 8) of approximately one-half of the standard diameter and arranged the ports in a unique double row, "lazy Z" or zig-zag pattern. This smaller diameter, 16-hole zig-zag pattern provided flow rate increases of approximately 15% to 20% in comparison to the previous designs as described above when tested with identical throat diameters under identical pressure conditions. As a result, this modified high flow PRV reduced the quantity of PRVs needed in a given inflation device and supplied improved flow rates at a lower operating range.
However, the additional ports add additional cost to each PRV because each port must be bored and deburred--both of which are time consuming and cost adding processes. In addition, the industry continues to seek increased exhaust flow rates at lower operating pressures. These lower pressures reduce the stress on the raft fabric seams. The higher exhaust flow rates reduce the quantity of PRVs needed to accomplish such relief. It also continues to be desirable to provide "pop action" exhausting at between 2.0 to 2.5/2.8 psi rather than at higher pressures.